Most commercial synthetic marble, synthetic onyx, synthetic granite and the like has been heretofore made with inorganic particulate filler in a resin matrix. The inorganic filler is usually a finely ground aluminum trihydrate, calcium carbonate or the like which has an angular surface due to the process of grinding. See, for example, U.S. Pat. Nos. 3,396,067, 3,433,860, 3,773,886, and 4,343,752. Polyester resin filler has also been used, also in ground form, such as in U.S. Pat. Nos. 2,987,496, UK Patent No. 1,174,952 to Majnoni, U.S. Pat. Nos. 3,966,669, 4,159,301 (col. 6, lines 29-43), and 4,137,215.
Prior to the present invention, it has been known to make polymer beads, and particularly unsaturated polyester beads, in a suspension process. E. R. Kolodny in U.S. Pat. No. 3,089,542, and E. L. Kropa in U.S. Pat. No. 2,443,735 disclose methods for preparing polyester beads in suspension; Buzbee and Lake, U.S. Pat. No. 3,823,202, discuss some of the important variables to control in the preparation of clear polymer beads. They disclose the addition of salts to the suspension mixture to improve the clarity and reflectivity of the beads (see also Buzbee and Hite U.S. Pat. No. 3,877,787). M. Narkis, J. Appl. Polymer Sci. 23, 2043-2048, (1979), discusses some of the operational variables in making such polyester beads by suspension polymerization. Spherical resins are also described in U.S. Pat. Nos. 3,929,685, 3,989,775, and 4,398,003.
Various suspending media have been proposed see U.S. Pat. Nos. 3,986,992 (Re. No. 29,555) and 4,025,484. U.S. Pat. No. 3,707,585 employs an acrylamide/acrylic acid ester. However, prior workers in the art have not directed their attention to the need for controlled particle size (however, see U.S. Pat. No. 3,728,318 which strives for uniformity) while also minimizing or eliminating, as far as possible, the incidence of hollow beads, enhancing the ability of the beads to adhere to a matrix throughout the stress of cure, and still provide an efficient suspension process.